The foremost of the Hyborean kingdoms, situated east of the Pictish wilderness, west of Nemedia, north of Zingara and Ophir, and south of Cimmeria.
Aquilonia has a pleasant, temperate climate (like that of modern France or Germany). The Border Range of Nemedia naturally delineated its borders on the east, the thickly forested hills of Cimmeria to the north, the large Thunder River to the west, and the Tybor River in the south. Another area of rugged mountains arose in the southern province of Poitain, which was flanked by the Alimane and Khorotas Rivers.
The frontier region of Westermarck between the Thunder and Black Rivers was thinly settled and beleaguered by Picts. Certain barons sponsored its provinces of Oriskonie, Conawaga, and Schohira. Thandara was independent. East of the Thunder River and curving northward toward the Cimmerian lands lay the narrow buffer province called the Bossonian Marches, or Bossonia. The nobles of Aquilonia were apparently not able to extend their sway over the staunch villagers of this region.
Another enclave that resisted the power of Aquilonian nobility was Gunderland in the far northwestern hills. Its ancient people, of the purest Hyborean stock, "never considered themselves exactly Aquilonians.”
Among the other provinces or counties mentioned in the Saga were Pellia (the only region ruled by a prince), Tauran, Couthen, Manara, Thune, Raman, and Karaban. Baronies mentioned include Kormon, Torh, Amilius, Lor, Imius, and Attalus.
The capital of Aquilonia was Tarantia, lying on the Road of Kings, the main east-west trade route of the Hyborian world. Interior Aquilonia was well drained by the rivers Shirki, Khorotas, Ossar, Fury, and the presumed Valkia. East of the Shirki and extending nearly to the foothills of the Border Range of Nemedia lay fertile plains interspersed with "tame" woodlands.
Much of the good cropland is sequestered by the aristocracy for use as hunting preserves, forcing the expanding population into risky colonizing ventures in Westermarck.
The history of Aquilonia is complex. We have assumed, after considering both historical and geographical factors, that Aquilonian Acheron fell to invading Hybori some time after Nemedian Acheron. With the establishment of a Hyborian kingdom in Aquilonia, the nation became "supreme in the western world", the most powerful from a commercial and military standpoint -- though perhaps second to Nemedia in cultural richness.
Aquilonia's royal house is heading toward a state of decadence and the Westermarck region on the verge of revolt.
Poitain, while under the protection and province of Aquilonia, is very much a unique and separate culture. They are best known for their prowess in raising and training griffons for scouting and use in battle. Roughly a century ago Poitain discovered the existence of these rare, magnificent creatures and quickly capitalized on their luck, keeping the existence of the creatures hidden while training their own people on how to raise and tame them. This gave Poitain a decided advantage over other regions, increasing the value and worth of the province as a whole. The barons and counts leveraged this unique boon with the Aquilonian leadership to maintain a level of sovereignty that provided freedom not usually afforded to other Aquilonian provinces. The most renown group of griffon fighters is the Order of the Silver Wing. Warriors and generals come from all corners of the map to trade and learn how to fight with the Silver Wing griffons. Wealthy aristocrats likewise travel far distances and pay huge sums of gold to buy one of these rare treasures, although the Order of the Silver Wing has a well established history of denying merchant groups the privilege of purchasing these majestic creatures who will ultimately only be put on display by the aristocrats. These creatures are prohibitively expensive, ensuring only those who are truly dedicated to their care and protection make the investment. The griffons must be matched properly with their rider or the required bond will not be forged and the individual will be powerless to control the creature. This advancement in mounted combat has served to guarantee the province of Poitain a place in the world history books.
Humans and halflings are the most common races in Aquilonia. Although most halflings start out in Aquilonia, the vast majority of them end up scattered around the map, acclimating themselves with the different cultures and societies.
References: Hyborian Age I-II, Tower of the Elephant, Hall of the Dead, Queen of the Black Coast, Red Nails, Beyond Black River, Treasure of Tranicos, Wolves Beyond the Border, Hour of the Dragon, Conan of the Isles, Conan the Liberator, Conan the Great, Conan the Rogue, Conan and the Death Lord of Thanza, et al.